Many medical imaging procedures utilize X-ray radiation because X-rays are of energies, or wavelengths, that can penetrate most human tissue but are also absorbed or scattered to differing degrees by relatively dense tissue of organs and by bone. This property is useful as the relative intensity of X-rays emerging from a given irradiated region of a patient will correspond to the “X-ray density,” i.e., the propensity to attenuate X-rays, of the internal structures within that region. Collected by an X-ray detector or simply incident on a fluorescent screen or X-ray film, emerging X-rays can be used to image the internal structures of the region. Furthermore, implements such as catheters may be inserted into a patient for surgical purposes and be tracked using X-ray imaging, or X-ray dense fluids may be injected into patients' veins so that blood vessel networks can be highlighted in subsequent X-ray images.
Some X-ray imaging procedures irradiate the patient for only a short period of time, as less than a second may be required to collect enough intensity data for a single X-ray image. However, some X-ray imaging is completed on a continuous basis such that a real-time video is generated for fluoroscopy and other image-guided procedures. Many surgeries, including the placement of stents and other cardiac procedures, have become much safer and requiring of significantly less recovery time since real-time X-ray imaging systems have enabled less invasive procedures.
While X-ray imaging is widely used for the aforementioned reasons, health risks associated with excessive exposure to high energy radiation, including X-rays, are recognized. The interaction of radiation with human cells and tissues may induce breakages or mutations which can develop into cancers over time. The probability of this type of cellular damage may be relatively insignificant from the exposure necessary to take a single image, as may be necessary to analyze a broken bone, but may become less insignificant for patients who undergo relatively lengthy image-guided procedures, require multiple CAT scans, or undergo other multi-frame X-ray imaging procedures. Furthermore, cumulative amounts of scattered X-ray radiation may pose health risks for medical personnel attending X-ray imaging procedures on a regular basis.
Precautions taken in medical settings against significantly increasing individuals' cancer risk through X-ray exposure have included attaching collimation devices to X-ray sources which attenuate X-rays travelling in directions away from the region to be imaged and providing physical shielding for attendant personnel. Use of non-conventional X-ray imaging configurations such as inverse geometry systems have been explored to lower the overall amount of X-ray exposure necessary to obtain good-quality X-ray images by reducing scatter noise or other factors that degrade image quality.
However, existing precautions do little to tailor the amount of X-ray radiation being used during an imaging procedure to the specific patient, or regions within the patient, to reduce the amount of radiation exposure. What is needed is an imaging system capable of producing rapid high quality images while reducing the amount of radiation exposure.
Use of beam hardening filters, which may filter out a number of the lowest energy components of an X-ray energy spectrum, is another method that has been explored for reducing exposure and improving image quality. However, such filters can only remove the relatively lowest energy X-rays and can be difficult to implement effectively. What is needed is an X-ray source providing a relatively monoenergetic spectrum of generated X-rays. What is further needed is an X-ray source capable of providing such an X-ray beam with a well-defined focal spot. Such an X-ray source could enable further applications of X-ray technology in the medical, security, metrology, and other fields.